Rocking electric tube furnace



Dec. l0, 1968 J. c. McMuLLl-:N 3,415,940

ROCKING ELECTRIC TUBE FURNACE 3 Sheets-Sheet l Filed March 15, 1967 d 4M w/ 0 il-, w M 6 6 3 4 L lu ,n|l.||o u I l I I l l ||.T.. 6 .d v M 5 .M2 e 9 3/ 3 f V 6 9 u 4 w m 3 4 6 .1o Il -lll 4 ...ln -M nno Ik 'II'I 2.992 4 6 2 5 H 2 A vso FIG.

INVENTOR. JOHN C.' MCMULLEN Dec. l0, 1968 J. c. MCMULLEN BOOKINGELECTRIC TUBE FURNACE 3 Sheets--Sheeil 2 Filed March 16, 1967 FIC5.2l

INVENTOR JOHN C. McMULLEN Dec. l0, 1968 J. c. MCMULLEN ROCKING ELECTRICTUBE FURNACE 5 Sheets-Sheet 5 Filed March 16, 1967 FIG.3

INVENTOR. JOHN C. McMULLEN g/MM United States Patent 3,415,940 ROCKINGELECTRIC TUBE FURNACE John C. McMullen, Niagara Falls, N.Y., assignor toThe Carborundum Company, Niagara Falls, N.Y., a corporation of DelawareFiled Mar. 16, 1967, Ser. No. 623,661 Claims. (Cl. 13-21) ABSTRACT 0FTHE DISCLOSURE An electric tube furnace for heat treating granularmaterials having means for tilting a resistance tube heater downwardlytowards the discharge outlet of the resistance tube and a crank drivemechanism for rocking the resistance tube aibout its longitudinal axisto continuously advance the granular material through the resistancetube toward the discharge outlet. Flexible electrical conductor cablesare employed to deliver a high amperage current to the resistance tube.

This invention relates to electric furnaces and, more particularly, to acontinuous, high temperature, rocking tube lfurnace.

In the field of heat treating granular material, such as iabrasive graincompositions by way of example, it has been known to employ rotarycontinuous tube furnaces in which the tube furnace is revolved through360. In this manner, the granular material is continuously advancedthrough the furnace to prevent the grain material from adhering togetherand to provide a short contact time at the desired temperatures in orderto prevent undue crystal growth.

Although such prior known furnaces have served the purpose for 'whichthey were designed, they have not been entirely satisfactory under allconditions of operation due to their inability to maintain controlledhigh temperatures and electric contact at the opposite ends of the tubeto handle the large amperage required in the heat treating and sinteringof certain abrasive grains.

Summary of the invention The general purpose of this invention is toovercome the above disadvantages by providing a furnace for heattreating granular material continuously under controlled conditions oftemperature, atmosphere and contact time.

Means are provided Ifor rocking the tube furnace to r effect continuousmovement of the granular material while simultaneously permittingeffective electrical contact at each end of the tube furnace toaccommodate a high current input.

Accordingly, it is an object of the present invention to ICC taileddescription thereof when taken in conjunction with the followingdrawings, in which:

FIG. l is a side elevational view of the electric tube furnaceconstructed in accordance with the principles of this invention;

FIG. 2 is a front end elevational view of the structure shown in FIG. 1lwith the feeding mechanism removed;

FIG. 3 is a longitudinal sectional view taken on the plane of line 3 3of FIG. 2 illustrating the discharge end of the furnace and with partsremoved to more clearly illustratethe interior of the furnace; and

FIG. 4 is a longitudinal sectional view of another embodiment of theinterior of an electric tube furnace constructed in accordance with theprinciples of this invention.

With reference to FIG. l of the drawings, it will be seen that anelectric tube furnace constructed in accordance with the principles ofthis invention comprises a shell or casing, generally designated .10',of either a square or rectangular cross section and preferably formed ofasbestos board. For purposes of this description, the forward or frontend of the furnace is taken to be the entrance or left end of thefurnace as seen in FIG. 1. Casing 10 is provided with a forward end slab12 and a rear end slab 14 preferably [formed of graphite and eachconsisting of two half sections 16 and 18 (see FIG. 2) havingsemi-circular grooves 20 and 22, respectively, that form a circularopening for receiving and supporting yan elongated hollow cylindricalresistance tube 24, preferably made of graphite, which protrudes beyondsaid front and rear end slabs. Resistance tube 24 is provided with aninlet end 25 at the forward end of the tube and an outlet or dischargeend 27 at the rearward end of said tube. A thin strip 23 of ceramicfiber is positioned between the edges of the slabs facing each other andacts as a seal therebetween to prevent the ambient air from enteringinto the interior of the casing 10.

The interior space A26 of the casing 10 surrounding the resistance tube24, is filled with a particulate mass of thermal insulating material,such as carbon black by way of example, -which serves as a thermalinsulator and Ialso prevents oxidation of the exterior surface ofresistance tube 24.

vCasing 10 is rigidly secured onto a cradle, generally designated 28,having a pair of upper inverted U-shape brackets 30 located adjacent theends of casing 10 and a pair of semi-circular tracks 32 rigidly securedto said brackets, respectively, by any suitable means. .A plurality ofstructural braces 33 are suitaibly rigidly secured to and extend betweentracks 32. Since the tracks are of identical construction and functionin the same manner, it is believed that a detailed description of onlyone will sulice, it ibeing understood that the same reference characterswill be applied to identical elements. Track 32 is of an angled crosssection and comprises legs 34 and 36. The side of the leg 36 facing tube24 is rigidly secured to a pair of structural angle members 38 and 40Iwhich in turn are rigidly secured to Ea reinforcing support member 42mounted on the bottom of casing 10. The other side of leg 36 is adaptedto ride on cam rollers 44 to Ifacilitate the lateral rockin-g movementof casing 10 as will be hereinafter more fully explained. Rollers 44 arejournaled for rotation on support members `46 located at either end ofthe furnace and carried by a frame 48 supported on a pair of suitablestandards or pedestals 50 at the rearward end of the frame and a pair ofhydraulic jacks `52 at the forward end of the frame. Thus, any desiredslope of the furnace can be attained by selectively raising or loweringthe forward end thereof. Alternatively, frame 48 may be mounted on fourrollers for easy transportation, if desired, with four jacks locatedadjacent to theV rollers, respectively, and engageable with a groundsurface to lift the rollers from the ground surface when the furnace isto be kept stationary.

Since the furnace is adapted'to be tilted so that the casing is inclinedin a downward rearward direction, some means are necessary to preventthe casing 10 from sliding axially in such direction. Accordingly, a camroller 54 rotatable about a substantially vertical axis abuttinglyengages leg 34 of track 32 to prevent axial rearward movement of casing10 while permitting rocking movement thereof. Cam roller 54 is journaledfor rotation on bracket 56 rigidly secured to support mernlber 46.

Means are provided for rocking or oscillating easing 10 about itslongitudinal axis relative to frame 48. Such means comprises a motor 58suitably mounted on frame 48 and having a power shaft 60 to which isrigidly secured a drive pulley 62. A drive belt 64 extends between drivepulley 62 and a driven pulley -66 to rotate shaft 68 connected to asuitable gear reduction mechanism 70 having a suitable output shaft 72.

An elongated drive arm 74 is suitably rigidly connected at one end tooutput shaft 72 and at the other end to a bolt 76. An elongatedconecting rod 78 has a rod end bearing 80 at one end thereof pivotablyconnected to bolt 76 and a rod end bearing 82 at the'other end pivotablyconnected to a bolt 84 rigidly secured to an upstanding post 86 rigidlysecured to support member 42. A spacer 88 separates rod end bearing 80from drive arm 74 and a spacer 90 separates rod end bearing 82 fromupstanding post 86. Thus, it will be seen that rotation of output shaft72 rotates drive arm 74 and by means of connecting rod 78, effectslateral oscillating movement of casing 10tabout the longitudinal axis oftube 24 relative to frame 48, to advance granular material through theresistance tube. Friction is held to a minimum by the use of tracks 32and cam rollers 44.

The graphite front and rear end slabs, 12 and 14, respectively, act aconductors and make electrical contact adjacent the forward and rearwardends of resistance tube 24 for the purpose of heating the same. A pairof water cooled terminal Iblocks 92 and 94 are suitably mechanically andelectrically connected to graphite slabs 12 and 14, respectively.Flexible insulated conductor cables 96 and 98 carry current to terminalblocks -92 and 94 from a suitable source of electric power (not shown).A range of 3.3 to 12.3 volts is made available to the furnace throughsuitable step-down transformers (not shown) 'and due to the lowresistance of the graphite resistance tube 24, the amperage input mayreach as high as 3000 amperes. Because the furnace is rocked oroscillated up to approximately 132 rather than completely revolved 360liexible cables 96 and 98 can be employed to accommodate the highamperage power rather than using troublesome sliding contacts whichwould be required if the furnace or tube were completely revolved. y

It should be noted that the resistance tube includes a central heatingsection or hot zone portion and cold ends adjacent end slabs 12 and 14.The hot zone is substantially midway of the resistance tube and has alength of approximately 1/7 of the length of the tube in the specificembodiment described. These relative lengths are set forth forillustrative purposes only and are not intended to restrict or limit thescope of this invention.

In order to maintain the resistance tube 24 relatively cool adjacent theterminal portions, means are provided for cooling the end slabs 12, 14andterminal blocks 92, 94. Since the cooling means employed to cool theforward and rearward ends of the furnace are identical, it is believedthat a detailed description of the cooling means for the forward endonly will suice. Such means comprise a conduit 100 leading from'asuitable source (not shown) of coolant, such as waterfor example, bymeans of a exible hose 102, said conduit 100 passing through terminalblock 92. With reference to FIG. 2, it will be seen that after leavingterminal block 92, conduit 100 is directed horizontally through slab 12in a direction normal to the longitudinal axis of resistance tube 2-4,then along the front of said slab and wrapped about the periphery oftube 24 as at 104, then back through the bottom portion of slab 12 in areverse direction and back to the source through a suitable exible hose106.

Means are provided for delivering granular material to the graphiteresistance tube 24 and comprises a charging funnel type hopper whichgravity feeds material onto a feeder pan 112 connected to a vibrator 114carried by a support 116 which is connected to a structural supportcolumn (not shown). The granular material is fed onto the feeder pan 112at a controlled rate by vibratory movement of said pan, through thespout 118, `and into the inlet end of resistance tube 24. The feed ratemay be adjusted by a rheostat control located on the vibrator 114 and/or by adjusting the angle of inclination of the feeder pan 112.

The contact time of grain in the hot zone of resistance tube 24 can bevaried from about 1 minute to 8 minutes or more depending on the degreeof tilt of resistance tube 24 and the rate of feed. Casing 10 andthereby resistance tube 24 can 4be tilted at any angle of inclinationdesired by actuating jacks v52. The maximum feed rate withoutoverloading is dependent upon the degree of tilt of resistance tube 24.At any given feed rate there is a minimum angle of tube tilt that can betolerated and any lesser degree of tilt will result in part of the feedmaterial falling out of the inlet end.

With reference to FIG. 3, an aperture 120 is provided in resistance tube24 in the area of the hot zone to accommodate the outlet end of a tube122. During normal operation of the furnace, granular material is fedinto the inlet end of resistance tube 24 and tube 122 is closed by meansof a plug 124. However, under certain conditions, it is desirable tofeed granular material directly into the hot zone in which event, plug124 is removed and the material fed through tube 122.

As shown in FIG. 3, an opening 128 is provided in resistance tube 24adjacent the forward end thereof, said opening communicating with apassageway 130 having an internally threaded end portion foraccommodating connections for conduits which deliver selected inertgases to the tube from a suitable source. Normally, when the furnace isused as shown in FIG. 3, passageway 130 is closed off by a suitable plug131.

As shown in FIG. 3, a gas tight metallic cover 133 is mounted over theoutlet end of resistance tube 24. A graphite ring 135 is provided withincover 133 in abutting relationship with the end of resistance tube 24and acts as a bearing against which the end of tube 24 may rock relativethereto. A gas inlet 137, such as an elbow type fitting for example, isrigidly secured into the end wall of cover 133 and is provided with athreaded end portion for accommodating connections for conduits whichdeliver selected inert gases to the tube from a suitable source (notshown). A funnel spout 138 is provided in the bottom of cover 133 forpermitting discharge of the granular material into a suitable gas tightreceptacle 139. An inert gas is introduced under pressure throughfitting 137 and is exhausted through the inlet end of resistance tube24. A porous graphite ring 140 is provided at the inlet end ofresistance tube 24 and disposed about spout 118 to preclude the ambientair from entering into said tube while permitting the inert atmospherein the resistance tube 24 to bleed out therethrough. Spout 118 fitsloosely within graphite ring 140 to permit relative rocking motiontherebetween. Alternatively, a suitable burner ring may be employed atthe inlet end of resistance tube 24 to prevent oxygen from entering intosaid inlet end.

In operation, the furnace is tilted at the proper angle of inclinationin accordance with the contact time of grain desired in the hot zone.The rate of feed of material into the resistance tube is adjusted byeither tilting feeder pan 114 and/or controlling the vibratory motion ofsaid pan by means of a rheostat control. Electric current,is supplied tothe resistance tube from a suitable source `by means of cables 96, 98,terminal blocks 92, 94, and graphite slabs- 12, 14. Motor 58 is startedto effect rotation of the crank drive mechanism and thereby cause thecasing and resistance tube 24 to be rocked or oscillated about thelongitudinal axis thereof. FIG. 2 illustrates in phantom the position ofthe casing 10 when the connecting rod 78 has substantially reached t-heend of its throw. Preferably, the furnace is given an oscillation of 132'but this may be adjusted, as desired, by simply changing the effectivelength of the connecting rod 78 by means of its threaded end portions.

The combined effect of the tilting orientation and the rocking motionapplied to the tube furnace advances material continuously at acontrolled rate through the furnace from the inlet end, through the hotzone and ultimately to the outlet end. When conditions warrant, materialmay be fed directly to the hot zone by means of tube 124. During thepassage of material through the resistance tube, a non-reactiveatmosphere is maintained in the resistance tube by introducing asuitable inert Igas through the gas inlet 137.

As a result of this invention, an improved electric furnace is providedfor treating granular material continuously under controlled conditionsof contact time in the hot zone, temperature and atmosphere in animproved and more efficient manner. By the provision of tilting meansand means for rocking or oscillating the casing and thereby theresistance tube, granular material is continously advanced through thetube furnace while permitting the high amperage power input necessary toeffect the heat treating operation. This high amperage current isdelivered to the resistance tube through flexible cables. Anotheradvantage residing in the use of the furnace of this invention is thatmaterial can be fed directly into the hot zone, an expedient which couldnot be accomplished with a rotary furnace.

FIG. 4 illustrates another embodiment of the electric furnace of thisinvention which is very similar to the above-described embodiment withthe exception of providing an insert tube within the graphite resistancetube and eliminating the metallic cover of the outlet end 0f the tube.All of the other structural features and their resultant functions areduplicated as disclosed in the embodiment of FIGS. 1 3 and the samereference characters primed are used to identify elements whichv aresimilar to those employed in the first embodiment.

With reference to FIG. 4, it will ybe seen that an elongated, thinwalled, impervious, refractory insert tube 134, preferably made ofalumina, is encased within resistance tube 24. An opening 136 isprovided in the wall of the tube 134 for accommodating tube 122. A longstaple inorganic, permeable, ceramic fibrous material 142 is positionedbetween insert tube 134 and resistance tube 24' adjacent the oppositeends of said insert tube to preclude the'ambient air from enteringtherebetween and since the inert atmosphere introduced throughpassageway 130 and opening 128 to prevent oxidation of resistance tube24 is at a greater pressure, it may ybe slowly exhausted through thepermeable material 142. Moreover, the ceramic fibrous material 142 alsoacts as a support in positioning insert tube 134 within resistance tube24.

The advantage residing in the second embodiment is that the insert tubecan -be utilized under oxidizing and neutral conditions. Under reducingconditions the insert tube can be removed and the graphite tube alonecan be used. It will thus be seen that the furnace may be en ployed inany atmosphere from oxidizing to reducing.

Although the above embodiments were described i connection with aresistance tube type heater, it shoul be appreciated that the principlesof this invention cor template the use of an inductively heated tube inwhic. an induction coil may be wrapped about the graphite tub andenergized to heat the same.

Preferred embodiments of the principles of this inven tion having beenhereinabove described and illustrated, i is to be realized thatvariations and designs may be ap plied without departing from the broadspirit and scope of this invention as defined in the appended claims.

I claim:

1. An electric furnace comprising: a frame; a cradle movably supportedon said frame; a casing carried by said cradle andmovable therewith; agenerally horizontally disposed refractory tube -havinrg a longitudinalaxis and mounted in said casing for movement therewith, said tu-behaving a material inlet end and an outlet end; means for electricallyheating said tube; means ,on said frame for adjustably tilting saidcasing and said tube downwardly along the longitudinal axis thereoftoward the outlet end of said tube; and means for oscillating saidcradle, casing, and tube about the longitudinal axis of said tube.

2. An electric furnace as defined in claim 1 in which said tube iscomposed of graphite.

3. An electric furnace as defined in claim 2 in which electricalcontacts are provided for said tube whereby to supply electrical currentto said tube and heat it by its resistance.

4. An electric, furnace as defined in claim 3 including a substantiallygas-tight cover encasing and adapted for relative rotary `movement withrespect to the outlet end of said tube.

5. An electric furnace as defined in claim 4 including a gas inlet insaid gas-tight cover for providing an inert atmosphere in said tube. Y

6. An electric furnace as defined in claim 5 including means adjacentthe inlet end of said tube for precluding the admission of air into saidtube while permitting the bleeding off of said inert atmospheretherethrough.

7. An electric furnace as defined in claim 2 in which said tube isprovided with a refractory ceramic lining.

8. An electric furnace as defined in claim 7 in which said lining is inthe form of a refractory ceramic tube and refractory ceramic fibrousmateriall is positioned around said refractory tube and within saidgraphite tube adjacent the endsy of the latter.

V9. An electric pfurnace as defined in claim 8 in which an inert gasinlet is provided in said gljaphite tube t0 provide an inert vatmospherebetween said'` graphite tube and said refractory ceramic tube. f

10. An electric furnace as defined in claim 8 in which said refractoryceramic tube has a second material inet intermediate said first materialinlet end and said outlet end.

11. An electric furnace as defined in claim 1 in which a particulatemass of thermal insulating material is deposited between said tube andthe interior surface of said casing.

12. An electric furnace as defined in claim 1 in which said tube has asecond material inlet intermediate said material inlet end and saidoutlet end.

13. An electric furnace comprising a frame; a cradle movably supportedon said frame; a casing movable with and carried by said cradle; algraphite tube 4mounted in said casing for movement therewith and havingits longitudinal axis generally horizontal, said tube having a materialinlet end, an outlet end, and a second material inlet intermediate saidends; a particulate mass of thermal insulation within said casing aroundsaid tube; means for supplying electrical current to said tube wherebyto heat said tube by its own resistance; means for supplying an inertgas to the interior of said tube; means for adjusttbly tilting said tubewhereby to change its inclination to he horizontal; and means foroscillating said cradle, zasing, and tube about the longitudinal axis ofsaid tube.

14. An electric furnace as defined in claim 13 in which iaid graphitetube is provided with a refractory ceramic ming.

15. An electric furnace as defined in claim 14 in which said lining isin the form of a refractory ceramic tube and refractory ceramic iibrousmaterial is positioned around said refractory tube and within saidIgraphite tube adjacent the ends of the latter.

References Cited UNITED STATES PATENTS 1,009,559 12/1911 Peacock 13-21 51,249,854 12/1917 Tanzer 13-21 1,449,834 3/1923 Pehrson 13-21 2,156,2635/1939 Kusaka et al 13-21 2,143,197 1/1939 Lang 13-21 ROBERT K. SCHAFER,Primary Examiner. 10 M. GINSBURG, Assistant Examiner.

